Genetics

Punnett Squares

• Used to determine possible outcomes of offspring. 

• Study Monohybrid, dihybrid, polyhybrid Punnett squares. 

• Punnett Squares help you solve Monohybrid and Dihybrid crosses. 

• P=Purple, p=white. 

1. PP= homozygous dominant

2. Pp=heterozygous

3. pp= homozygous recessive

4. The combinations of alleles are called genotypes, the physical characteristics that result from them are phenotypes. 
   

• When writing ratios and percents, it goes homozygous dominant: heterozygous: homozygous recessive. 

Sex-Linked Traits

• ✅Mostly affects males

• C=Normal

• c=color-blind

• X^C Y is a normal Male.

• X^c Y is a color-blind male. 

• X^C X^C is a normal female. 

• X^C X^c is a carrier female, but not affected. 

Blood Types

• A= I^A I^A and I^i or AA AO

• B= I^B I^B and I^i or BB BO

• AB= I^A I^B or AB (Codominance)

• O= ii or OO

• O is a recessive trait. 

Pedigrees

• Pedigrees are used to trace the inheritance of traits through generations, helping to identify carriers of recessive alleles.

• How can you tell if a trait is Autosomal D or R, or sex linked?

• Males are carriers in autosomal traits, but not sex linked. 

• In sex linked traits, Males either do not have the allele or they are affected. They can’t be a carrier. 

• Autosomal Recessive: both males and females are affected equally, it can skip generations, and that two unaffected parents can have an affected child (for example, if both parents are carriers, represented as Aa, they can have an affected child with the genotype aa).

• Autosomal Recessive Pattern: 

1. ✅Affected individuals inherit one recessive allele from each parent

2. ✅Recessive traits are only expressed in homozygous individuals

3. ✅Alleles segregate randomly during gamete formation

• Autosomal Dominant: 

1. ✅ Both males & females affected equally

2. ✅ At least one affected parent

3. ✅ Does not skip generations

A trait that is expressed if at least one dominant allele is present in the genotype (either AA or Aa). 

• Sex Linked Traits: 

• ✅There will be a lot more males affected than females.

Mendel's Laws

Mendel's laws of inheritance describe how traits are passed from parents to offspring. They include:

1. Law of Segregation: During gamete formation, the two alleles for a trait segregate from each other, resulting in each gamete carrying only one allele for each trait.

2. Law of Independent Assortment: The alleles for different traits assort independently of one another during gamete formation, meaning the inheritance of one trait does not influence the inheritance of another, as long as the genes are on different chromosomes.

3. Law of Dominance: When different alleles are present, one may dominate the other, leading to the expression of the dominant trait.

4. Incomplete Dominance: A situation where the phenotype of heterozygotes is intermediate between the phenotypes of the two homozygotes.

5. Codominance: Both alleles in a heterozygote are fully expressed, resulting in a phenotype that displays both traits simultaneously (e.g., blood type AB).

6. Multi-allelic Traits: Traits controlled by more than two alleles, such as ABO blood types.

7. Polygenic Inheritance: Traits that are controlled by multiple genes, leading to a continuous range of phenotypes, such as height or skin color.